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|---|---|---|---|---|---|
747,118 | [
"https://physics.stackexchange.com/questions/747118",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/354923/"
] | If I have an object <span class="math-container">$A$</span> rotating at an angular velocity <span class="math-container">$w$</span>, how would I calculate the linear velocity <span class="math-container">$v(x, y)$</span> of a certain point <span class="math-container">$r(x, y)$</span> in the object?
| Susan won't immediately acquire the sled's velocity. There will need to be a horizontal frictional force between the sled and Susan's backside after she lands on the seat in order to accelerate her to the speed of the sled. An equal and opposite force will decelerate the sled.
Since this won't happen instantly, if the ... | Newton's second law for a system tells that the net external force is equal to the mass of the system times the acceleration of the cenetr of mass.
For the case described in the OP the horizontal force is zero and this means that the horizontal component of the velocity of the center of mass does not change. The horizo... | https://physics.stackexchange.com |
90,757 | [
"https://electronics.stackexchange.com/questions/90757",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/27049/"
] | I've got much difficulties to find the footprint for the components I have in hand:
They don't have name (I buy them at somewhere similar to flea markets). Therefore, their proper footprints are unknown nor I don't know where to find such information. So far, I've been wondering if every component (such as resistor, c... | There are "standard" footprints for most IC packages, like DIP, SOIC, etc., but the library creators for the CAD programs may excercise their creativity in naming the footprints, so you may have to do some searching to find the appropriate footprint for your part.
When I first used Protel (now Altium), it seemed that ... | SMD components and to some extent, through hole components have standard foot prints. If you have the component's reel, it is usually written on it. If not, you can measure the component with a caliper.
As for photographs of SMD passive components, they do not have much use. All capacitors of a certain size look the s... | https://electronics.stackexchange.com |
116,483 | [
"https://math.stackexchange.com/questions/116483",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/23559/"
] | It has been so long since I have done division inside of radicals that I totally forget the "special rule" for for doing it. -_-
For example, say I wanted to divide the <code>4</code> out of this expression:
<blockquote>
$\sqrt{1 - 4x^2}$
</blockquote>
Is this the right way to go about it?
<blockquote>
$\frac{1... | There is, in fact, one rather important mistake there. 16 is not the square root of 4. If you replace '16' by'2' in your equation then it is all right. In general, if you divide by everything inside the square root sign by some constant then you should multiply in front by the square root of that constant.
| Square roots obey the rule $\sqrt{a\cdot b}=\sqrt{a}\cdot\sqrt{b}$ . You wanted to take the $4$ out of $\sqrt{1-4x^2}$. $1-4x^2=4\cdot\frac{1-4x^2}{4}$. So $\sqrt{1-4x^2}=\sqrt{4\cdot\frac{1-4x^2}{4}}=\sqrt{4}\cdot\sqrt{\frac{1-4x^2}{4}}=2\cdot\sqrt{\frac{1-4x^2}{4}}$. I think that's the best explanation I can give... | https://math.stackexchange.com |
435,419 | [
"https://physics.stackexchange.com/questions/435419",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/98414/"
] | Consider a spring with potential energy <span class="math-container">$U=\frac{1}{2} k x^2$</span>, where <span class="math-container">$x$</span> is displacement from equilibrium.
Hooke's law says the force <em>required</em> to move the spring is <span class="math-container">$F=kx$</span>.
From classical mechanics, we... | Hooke's law is actually <span class="math-container">$F=-kx$</span> which specifies that the force that the spring produces is always pointing away (opposite) from the direction of the displacement of the spring from the equilibrium position (taken as <span class="math-container">$x=0$</span> for simplicity). There is ... | The system is the spring.
Ignoring the two forces acting at the fixed end of the spring consider the two forces acting on the free end of the spring <span class="math-container">$\vec F_{\text{on spring due to external}}$</span>, the external force, and <span class="math-container">$\vec F_{\text{on external due to ... | https://physics.stackexchange.com |
144,006 | [
"https://dba.stackexchange.com/questions/144006",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/56050/"
] | I have this simple query:
I want to list something like this:
<blockquote>
Unidade1 \ PLaca1 \ Placa2 \ Placa3
Unidade2 \ Placa1 \ Placa2
</blockquote>
But I don't know how many placas a unidade will have.
I was trying to pivot like this:
<pre><code>SELECT [undiade], [placa1], [placa2], ..
FROM Table1... | made it, with something simple ( i'm really bad at programming :
<pre><code>Select main.unidade_id,
Left(Main.viaturas,Len(Main.viaturas)-1) As "Viaturas"
into #temp
From
(
Select distinct v2.unidade_id,
(
Select v1.placa + ',' AS [text()]
From fro... | As Julien mentioned, dyanamic sql will be your answer for this. Below is an example of using pivoting with an EAV system. It really helps with reading the data.
<pre><code>DECLARE @Cols NVARCHAR(MAX)
DECLARE @Query NVARCHAR(MAX)
DECLARE @ClassName NVARCHAR(50)
SET @ClassName = 'customer'
SELECT @Cols = STUFF((SELECT ... | https://dba.stackexchange.com |
382,660 | [
"https://electronics.stackexchange.com/questions/382660",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/192334/"
] | I am a Mathematical Person. So thinking from that perspective.
To make my question slightly more concrete. I was thinking of controlling a hobby servo through a Uart serial data stream.
I am inventing numbers for the purpose of communicating the idea.
<strong>CONTEXT:</strong>
Suppose a servo needs to be refresh... | In general any library written in C is probably not going to have information on how many clock cycles it takes to execute a function. The reason is that it depends on your compiler optimization settings, and which compiler you use.
Usually you can only tell from source code how long something is going to take if you... | Even with a RISC processor like this, where all instructions take the same number of cycles, it is going to be difficult if not impossible to determine the exact number of cycles (and thus time) of a given library routine. Especially considering the that every conditional decision within each library call may introduce... | https://electronics.stackexchange.com |
6,911 | [
"https://datascience.stackexchange.com/questions/6911",
"https://datascience.stackexchange.com",
"https://datascience.stackexchange.com/users/10522/"
] | I work for a bank. Most of our data is in the form of database tables. Would we benefit by implementing Hadoop? I am of the impression that Hadoop is more for a Distributed File System (unstructured data) as opposed to OLAP databases (Netezza)
| 'SQL' on Hadoop is very much a thing, though I use quotes since it's probably more accurate to say it's SQL-like. Some options for bringing SQL-like capabilities to Hadoop include Hue, Hive/bee (Heading towards Stinger? So punny Apache), Impala, SparkSQL (probably not a great solution for a bank given the possibility o... | I think you are referring to the HDFS part of Hadoop. If I'm correct, using Hadoop IMHO should not be considered as an alternative, but as a necessity. Hadoop answers the question : how can I take advantage advantage of the massive amount of data I have since I can't use it now as it is.
So yes, HDFS is a distributed... | https://datascience.stackexchange.com |
571,958 | [
"https://physics.stackexchange.com/questions/571958",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/262169/"
] | I was studying a course about Lie groups, Lie algebras and their representations (and classifications) when I encountered this statement :
<blockquote>
When a physical system admits symmetry, the observable form a representation of the group concerned. Lorentz and Poincaré groups are very important examples.
</blockquo... | If a quantum system admits a Lie symmetry group, this means that there exist a unitary strongly continuous representation of that Lie group acting in the Hilbert space of the system. The one-parameter subgroups are represented by one-parameter strongly continuous unitary (sub) groups. Stone's theorem proves that each s... | Physical symmetries are in particular a certain transformation of the system. Translations displace the system from a point to another point. Rotations rotate the system. In general, in order to make sense of this statement one needs to give a prescription for the way that this transformation acts on your description o... | https://physics.stackexchange.com |
288,925 | [
"https://softwareengineering.stackexchange.com/questions/288925",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/185912/"
] | While chasing a segfault around a complicated and grouchy c++ program I added several <code>//comments</code> and <code>cout</code> statements, but no 'actual' code. Then, suddenly, for no apparent reason the segfault vanishes.
I'm happy, but still a little worried, because I don't think I fixed anything and there was... | Getting a segmentation fault only happens when you have invoked <em>undefined behaviour</em>. And undefined behaviour means that the normal rules of a programming language don't apply: whatever the run-time system does is by definition OK, and you don't get to complain about it. It <em>might</em> even do the expected t... | Segfaults often are affected by whatever garbage happened to be in the memory you're erroneously trying to access. Adding a <code>cout</code> near the bug can change that. I've also had bugs that are dependent on what memory location a pointer happened to be assigned to. Move the pointer by adding "irrelevant" code,... | https://softwareengineering.stackexchange.com |
195,708 | [
"https://softwareengineering.stackexchange.com/questions/195708",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/61231/"
] | Why does Haskell have a built-in <code>if/then/else</code>, which is dependent on the <code>Bool</code> type, instead of having a simple library function? Such as
<pre><code>if :: Bool -> a -> a -> a
if True x _ = x
if False _ y = y
</code></pre>
| It's purely for the nice sugar of the <code>if</code>, <code>then</code>, and <code>else</code> keywords; in fact, GHC (with the <code>RebindableSyntax</code> extension enabled) will desugar the syntax by simply calling whatever <code>ifThenElse</code> function is in scope.
| It doesn't matter much ... to me it looks like if/then/else is not used very often nowadays. I find myself writing pattern guards instad of if .. then .. else.
From a syntactic point of view, though, it is nice to have
<pre><code>if expr1 then expr2 else expr3
</code></pre>
So you can write
<pre><code>if foo a then... | https://softwareengineering.stackexchange.com |
83,553 | [
"https://softwareengineering.stackexchange.com/questions/83553",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/27038/"
] | Should we create a database structure with a minimum number of tables?
Should it be designed in a way that everything stays in one place or is it okay to have more tables?
Will it in anyway affect anything?
I am asking this question because a friend of mine modified some database structure in mediaWiki. In the end,... | <strong>IGNORE</strong> the number of tables. Worry more about getting the <em>design</em> correct. If your major concern is quantity of tables, you should probably not be designing database systems.
If your friend only needed 8 tables, and the system works fine with that, then 8 is the correct number, and the remaini... | A database should have exactly as many tables as it needs. No fewer, no more.
| https://softwareengineering.stackexchange.com |
28,484 | [
"https://softwareengineering.stackexchange.com/questions/28484",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/8486/"
] | When is something language agnostic? Why is it called that?
| <em>Language agnostic</em> refers to aspects of programming that are independent of any specific programming language. At least, that's how I've heard it used for the last thirty years.
The word "agnostic" is derived from the ancient Greek for "don't know". So something which is "language agnostic" doesn't need to kno... | Paradigms or features that aren't applied to only one language.
| https://softwareengineering.stackexchange.com |
109,559 | [
"https://electronics.stackexchange.com/questions/109559",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/27067/"
] | What practical advantages could there be in using a logic NOT gate IC (e. g. schmit trigger hex inverters) when compared to a simple NMOS + pull-up resistor inverter? I want to invert the PWM output of an arduino, and I suspect using a dedicated inverter IC might be a bit overkill for that application.
| A NOT gate will use less power. This is because the pull-up and pull-down will both be complementary transistors. This means that when the input is high and the pull-down transistor is pulling the output low, the pull-up transistor will basically be an open instead of a resistor between power and ground.
| An inverter will give you more symmetrical drive (low-to-high and high-to-low). This will be important if you are using the signal to drive, for example, the gate of a MOSFET.
| https://electronics.stackexchange.com |
40,964 | [
"https://math.stackexchange.com/questions/40964",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/8808/"
] | Consider a symmetric matrix $A$ with non-negative integer coefficients. It appears that the geometric series $\sum_{i \geq 0}A^i$ will converge to a matrix $B$ if the spectral radius (the largest eigenvalue in absolute value) is less than 1.
I would like to extend this result to a case where the matrix doesn't have in... | In any Banach algebra with identity over $\mathbb C$, the spectral radius of $x$ is $\rho(x) = \lim_{n \to \infty} \|x^n \|^{1/n}$. If $|t| \rho(x) < 1$, the geometric series $\sum_{n=0}^\infty t^n x^n$ converges to $(1 - t x)^{-1}$. This is standard material that you can find in any text that discusses Banach alg... | As stated in my comment, the question is not clear, so this answer may not be relevant, but maybe it will be of some use.
Suppose $A$ is a square matrix with complex entries. Then there's an invertible matrix $P$ with $P^{-1}AP=J$ in Jordan form. Then $$\sum A^i=\sum(PJP^{-1})^i=P\left(\sum J^i\right)P^{-1}$$ so $\su... | https://math.stackexchange.com |
507 | [
"https://cardano.stackexchange.com/questions/507",
"https://cardano.stackexchange.com",
"https://cardano.stackexchange.com/users/1142/"
] | Can I send 1 lovelace (0.000001 ADA) to another address or is there a minimum amount I need to send?
Of course there will also be the transaction fee of (currently) ~0.16 ADA, so such a transaction would not make much sense in most cases. Still I'm curious if it would work.
| There is a minimum UTxO transaction size of 1 ADA not including fees. That means the absolute minimum transaction is <code>1 ADA + fees</code>.
| In addition to fees (<code>txFeePerByte</code> + <code>txFeeFixed</code>) as shown in the protocol parameters below, you can see that there is as well a <code>minUTxOValue</code> field that specifies the lowest UTxO output.
Therefore, a transaction cannot contain less than <code>txFeePerByte</code> + <code>txFeeFixed</... | https://cardano.stackexchange.com |
9,452 | [
"https://dsp.stackexchange.com/questions/9452",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/4710/"
] | Suppose we know the DFT of a discrete limited sequence, some $X[k],\ k = 0, 1,\dots ,N-1$. How can we calculate the Fourier Transform of the same signal for a random frequency $\Omega$?
<strong>EDIT:</strong>
How about this, we can get the starting signal with inverse DFT, like: $$x[n] = \frac{1}{N}\sum\limits_{k=0}... | Your question makes perfect sense, yet your solution will not work. Note that the expression for $x[n]$
$$\begin{align}
x[n]=\frac{1}{N}\sum\limits_{k=0}^{N-1}X[k]e^{j\frac{2\pi}{N}kn} \end{align}$$
is periodic with period $N$. This means that the sum
$$
\frac{1}{N}\sum\limits_{n = -\infty}^{+\infty} e^{-j\Omega n}\... | There are an infinite number of continuous waveforms that have the same DFT after sampling, which then have different FTs. So you need to specify more. If some continuous signal you want is strictly band-limited, then Sinc interpolation will give you one smaller family of possible solutions from which you might be ab... | https://dsp.stackexchange.com |
534,117 | [
"https://math.stackexchange.com/questions/534117",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/101629/"
] | Prove that $1<\dfrac{1}{n+1}+\dfrac{1}{n+2}+...+\dfrac{1}{3n+1}$.
By using the Mathematical induction. Suppose the statement holds for $n=k$.
Then for $n=k+1$. We have $\dfrac{1}{k+2}+\dfrac{1}{k+3}+...+\dfrac{1}{3k+1}+\dfrac{1}{3k+2}+\dfrac{1}{3k+3}+\dfrac{1}{3k+4}=(\dfrac{1}{k+1}+\dfrac{1}{k+2}+\dfrac{1}{k+3}+..... | You are almost done. Prove that
$$\frac{1}{3k+2}+\frac{1}{3k+3}+\frac{1}{3k+4}-\frac{1}{k+1}$$ is positive.
To do this it is enough to show that $\frac{1}{3k+2}+\frac{1}{3k+4} \gt \frac{2}{3k+3}$. The left side can be written as $\frac{6k+6}{(3k+2)(3k+4}$. So we want to show that $(3k+3)^2\gt (3k+2)(3k+4)$.
| By cauchy-schwarz inequality
$$\left(\dfrac{1}{n+1}+\dfrac{1}{n+2}+\cdots+\dfrac{1}{3n+1}\right)(n+1+n+2+\cdots+3n+1)>(1+1+\cdots+1)^2=(2n+1)^2$$
note$$ (n+1+n+2+\cdots+3n+1)=\dfrac{(n+1+3n+1)(2n+1)}{2}=(2n+1)^2$$
| https://math.stackexchange.com |
664,438 | [
"https://physics.stackexchange.com/questions/664438",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/312912/"
] | If a relativistic rocket travels slower in time, does that mean the actual combustion in the thrusters happens slower and slower from an outside frame of reference? Is this part of what causes a relativistic rocket to lose acceleration from an outside frame of reference? Does this mean that an unfueled ship, such as on... | Yes, a vehicle with some constant power in it's rest frame would appear to have lower power from other frames.
<blockquote>
Is this part of what causes a relativistic rocket to lose acceleration from an outside frame of reference?
</blockquote>
The mechanism doesn't seem to matter to me. If I create a hypothetical veh... | <blockquote>
If a relativistic rocket travels slower in time, does that mean the actual combustion in the thrusters happens slower and slower from an outside frame of reference? Is this part of what causes a relativistic rocket to lose acceleration from an outside frame of reference?
</blockquote>
Of course. Slow motor... | https://physics.stackexchange.com |
619,989 | [
"https://physics.stackexchange.com/questions/619989",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/273770/"
] | If we consider two inertial reference frames <span class="math-container">$S$</span> and <span class="math-container">$S’$</span> where one moves with respect to the other at a velocity <span class="math-container">$v$</span>. If we find that in the reference frame S we have that the change in the kinetic energy of a p... | Your analysis is correct. In the case of one-dimensional motion with <span class="math-container">$0 \leq |v|$</span> the changes in kinetic energy of a particle traveling at speeds <span class="math-container">$V_1$</span> and <span class="math-container">$V_2$</span> w.r.t. the reference frame <span class="math-conta... | It is actually the total "energy-momentum" which is frame independent. Kinetic energy change is not frame independent. It is indeed frame dependant. The kinetic energy depends on momentum, where in units with <span class="math-container">$c=1$</span>, the total energy is given by <span class="math-container">... | https://physics.stackexchange.com |
429,800 | [
"https://physics.stackexchange.com/questions/429800",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/-1/"
] | In <em>Quantum Mechanics</em>, McIntyre states the projection postulate like so:
<blockquote>
After a measurement of <span class="math-container">$A$</span> that yields the result <span class="math-container">$a_n$</span>, the quantum system is in a new state that is the normalized projection of the original system ket... | The key point is
<blockquote>
[...] onto the ket (or kets) [...]
</blockquote>
When you measure observable $A$ and get result $a_n$, the corresponding eigenspace may have more dimensions than just one, i.e. you cannot speak of "the eigenstate $\left|a_n\right>$ corresponding to the result $a_n$. Hence, you real... | For a single particle I believe what you wrote is perfectly true, and the resulting state of the measure is indeed a phase times the eigenvector (although this phase does matter if your state is in a superposition, so you can't immediatly trash it).
I think maybe the principle was written this way however because it s... | https://physics.stackexchange.com |
71,728 | [
"https://chemistry.stackexchange.com/questions/71728",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/-1/"
] | <blockquote>
One mole of Van der Waal gas is compressed from $\pu {20 dm^3}$ to $\pu{10 dm^3}$ at $\pu{300 K}$. Given $a = \pu{3.60 dm^6 mol^-2}$ and $b = \pu{0.44 dm^3 mol^-1}$. Find $\Delta H$.
</blockquote>
<hr>
$\Delta H = -\mu C_p \Delta P + C_p \Delta T$
Since for VDW gas $ \displaystyle \mu C_p = {2a\over R... | As your book uses the terms:
<ul>
<li>Elements: Single atoms (e.g. O).</li>
<li>Compound: Consists of only one type of molecule, where that molecule consists of more than one element (e.g. H<sub>2</sub>O).</li>
<li>Mixture: Consists of more than one type of molecule (e.g. Na<sup>+</sup> + Cl<sup>-</sup> + H<sub>2</sub... | A good example of the difference might be to look at water, $\ce{H2}$, and $\ce{O2}$.
If you have gaseous $\ce{H2}$, and $\ce{O2}$ in a container you have a mixture; you can change it to have $99\%$ oxygen and $1\%$ hydrogen or vice versa or any ratio in between, but it is still a mixture of the two gases. These mixt... | https://chemistry.stackexchange.com |
297,082 | [
"https://physics.stackexchange.com/questions/297082",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/-1/"
] | The following statement is given in one of my physics textbooks:
<blockquote>
No work is done by a force on an object if the object moves in such a way that the point of application of the force remains fixed.
</blockquote>
But I could not think of any examples where object moves but the point of application of force r... | Consider the force exerted by a pivot (for example, at the top of the chain on a swing).
Clearly the pivot point does not move, hence $W=F.d=F(0)=0$ even though the force exerted by the pivot is nonzero ( or else the swing would fall to the ground).
| The Statement says that point of application does not move but you are saying that pivot does not move . pivot is not the point of application it is the point which applies the force.
| https://physics.stackexchange.com |
46,948 | [
"https://physics.stackexchange.com/questions/46948",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/7527/"
] | What is the significance of negative frequency in Fourier transform? Why we include the band widths of the negative frequency also while calculating band width of the signal.
| If you have a real function of time $x(t)$, which may represent, for example, a modulated carrier, you <em>can</em>, if you wish, avoid negative frequencies by using the <em>Fourier Sine Transform</em> $$X_s(\omega)=\int_{-\infty}^{\infty}{x(t)\sin\omega t dt} $$ and <em>Fourier Cosine Transform</em> $$X_c(\omega)=\i... | Choose a square root of negative one.
And now throw it out because statisticians hate complex numbers and negative frequencies, and never use them if we can help it. For us, the power spectrum really measures the variance of the data, we use the word «power» because these concepts were started by physicists and eng... | https://physics.stackexchange.com |
65,781 | [
"https://stats.stackexchange.com/questions/65781",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/15949/"
] | I'm trying to analyse some data from a set of bird surveys. My response variable is "bird abundance", which is the number of birds counted over a five-minute period. These five-minute counts were conducted at ~200 sites. Counts were repeated three times at each site, although there are ~20 sites where only two counts w... | There's nothing about a random or mixed effects model that requires having a certain number of observations per level. In fact, if you have many observations per level then the random effect may not be necessary and you may be able to just include that as a factor variable.
You should be able to just specify the site ... | you can include the sites with only two counts in your analysis.
One way is to create a multi-level model, assign prior distributions to all the observables and then use the data to update to the posterior distribution (essentially a bayesian analysis). For guidance, look at (Gelman, Hill 2006) and the tutorials for u... | https://stats.stackexchange.com |
363,232 | [
"https://physics.stackexchange.com/questions/363232",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/97775/"
] | The textbook I am following (Peskin&Schroeder) on QFT takes $\mathrm{d} \Omega = \mathrm{d} \cos \theta \mathrm{d} \phi$. I cannot for the life of me see that its correct. We know that $\mathrm{d}V = r^2 \sin \theta \mathrm{d}r \mathrm{d} \theta \mathrm{d} \phi$. But $\mathrm{d} \cos \theta = - \sin \theta \mathrm{... | Usually, you integrate $\theta$ from $0$ to $\pi$, but $\cos \theta$ from $-1$ to $1$ (P&S don't write the integration boundaries explicitly).
$$ \int_0^\pi \mathrm \sin\theta\, d\theta = \int_1^{-1} \mathrm d(-\cos\theta) = \int_{-1}^1 \mathrm d(\cos\theta) .$$
| I don't have the book at hand right now but my guess is that it is a case of
$$\int_0^\pi \sin\theta d\theta =\int_{-1}^1 d\cos\theta$$
| https://physics.stackexchange.com |
74,269 | [
"https://security.stackexchange.com/questions/74269",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/61573/"
] | Im curious about how secure a OpenVPN setup that uses a single cert/key to authenticate against the server, compared to a OpenVPN setup that uses a separate cert/key combination for each OpenVPN client.
The OpenVPN server configuration has a section that says I shouldn't be doing this, but is OpenVPN warning about pot... | There is no way of knowing who is connecting to your server. There's no attribution associated. If someone logs in and does something bad you'll have no way of knowing who it was, or narrow down where the security breach started.
Worse, you won't know if someone else steals the certificate, and accesses your server ... | You are basically narrowing your security to the username and password because your cert is single point of failure (if obtained it can be provided with any authorized credentials). Other thing you should take in consideration is impact of certificate revocation on your organization. Let's say you've found out that som... | https://security.stackexchange.com |
52,402 | [
"https://softwareengineering.stackexchange.com/questions/52402",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/18542/"
] | I'm writing a library to generate and check CSRF tokens.
I would like to do it without having to use sessions and/or cookies. What I've come up with is this:
<ol>
<li>A token generated from the current time and a unique token id (unix-timestamp.unique-token-id). </li>
<li>The token would then be hashed using the HMA... | If the token isn't tied to a particular session or cookie, then I (as an attacker) could write a script to harvest tokens, and embed them in my hosted pages. The token would then be passed by the victim's browser to your site and would validate correctly as it was generated by your server. (even though it's be for the ... | I'll argue with ach_l's answer, because I'm interested in the sessionless CSRF protection too :)
<blockquote>
(If the token isn't tied to a particular session or cookie, then I (as an attacker) could write a script to harvest tokens, and embed them in my hosted pages. The token would then be passed by the victim's b... | https://softwareengineering.stackexchange.com |
438,880 | [
"https://stats.stackexchange.com/questions/438880",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/159515/"
] | I have discrete data that comes from the distribution of a discrete random variable Y. The data appears to follow the normal distribution (ie if I make a kde plot it looks like a normal distribution). I've conducted Bayesian inference and assumed that the mean mu follows a normal prior. Thus, the posterior of mu also f... | It's true that you're not missing information when you use only <span class="math-container">$k-1$</span> categories. In linear models, we are all familiar with the dummy variable trap and the relationship between a model with <span class="math-container">$k-1$</span> levels and an intercept and a model with <span clas... | Go with your <strong>Option I</strong> - there is no need to do one-hot encoding when there are only two categories. <br> These two columns <code>Gender_M</code> and <code>Gender_F</code> carry the exact same information (since it's binary, at least in your example).<br>
I think some frameworks need binary <em>classes<... | https://stats.stackexchange.com |
1,473,513 | [
"https://math.stackexchange.com/questions/1473513",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/170605/"
] | The motion of a pendulum is described by the differential equation
<span class="math-container">$$ \ddot\theta +\frac gl \sin \theta = 0$$</span>
if we integrate this equation with respect to <span class="math-container">$\theta$</span> we obtain
<span class="math-container">$$ \frac 12 \dot \theta ^2 - \frac gl \c... | There is a tidy trick for that using <strong>chain-rule</strong>. Remember this once and for all. We have
$$\ddot \theta (t) + {g \over l}\sin \left( {\theta \left( t \right)} \right) = 0$$
where it is a <strong>nonlinear second order differential equation</strong>. Wow, it seems scary a little as we don't have <stro... | Multiply the equation through by $\dot{\theta}$:
$$\dot{\theta}\, \ddot{\theta} +\frac{g}{\ell} \dot{\theta} \sin{\theta} = 0$$
Integrate with respect to $t$.
$$\int dt \, \dot{\theta}\, \ddot{\theta} = \int d\dot{\theta} \, \dot{\theta} = \frac12 \dot{\theta}^2 + C$$
$$\int dt\, \dot{\theta} \sin{\theta} = \int... | https://math.stackexchange.com |
263,084 | [
"https://mathoverflow.net/questions/263084",
"https://mathoverflow.net",
"https://mathoverflow.net/users/94452/"
] | I have submitted a paper on applied probability in one of SIAM journals. The paper is under review for 9 months. I asked the editor 1 month ago about it, I was told that one review report has come and they are waiting for the other. Will it be ok if I politely inquire about it now (I have inquired 3 times till now afte... | My experience is in Pure Mathematics, not in Applied Probability. In my area, at least, it is unusual to have a full report recommending acceptance (pending revisions) in under a year, although it can happen much faster. It has happened to me within a few weeks, but that is the exception rather than the rule. My first ... | You have access to the journal through your institution, yes?
I suggest that you randomly selection some papers, from recent years.
Look at the date submitted. Also do consider how many times these were revised. This is a good proxy for how thoroughly the reviewers tend to scrutinize papers. It takes much longer to w... | https://mathoverflow.net |
538,993 | [
"https://electronics.stackexchange.com/questions/538993",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/22244/"
] | I downloaded a footprint for one IC from the internet.
It contained a .kicad_mod and a STEP file.
I have a directory where my project lives, so inside there are .pcb, .pro, .sch file and so on....
When i imported the library for my new foorprint, the new footprint's location is in a different directory of where my proj... | The board house is not interested in footprint files, they need either Gerber data from the "Plot" function or the <code>.kicad_pcb</code> board file, which contains copies of all footprints used, as you can modify them after placement (e.g. moving a silkscreen text that conflicts with another component).
The... | First of all, the above answer saying the PCB fab won't care is correct. But <em>you</em> should care for your own sanity, as you will have a large number of files to manage before long.
You can configure the footprints / models directory in several places
Go to Kicad main screen.
Open your project.
Option (1)
Menu->... | https://electronics.stackexchange.com |
8,873 | [
"https://security.stackexchange.com/questions/8873",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/-1/"
] | I hear stories about insecure web servers and sites which people (or bots) break into and execute their own code on the server.
My question is how is that possible? I heard of people putting their own javascript on websites stealing cookies and techniques how to do that. I never heard of actual attacks to execute code... | To be able to run code on your server, I could:
<ul>
<li>Upload a file using one of your web forms. But instead of an image, I upload a PHP file. Then I can run the code in the PHP file with the privileges of the webserver process.</li>
<li>Exploit a buffer overflow to get a shell on your server.</li>
<li>Log in as an... | The simplest would be a executable upload vulnerability. The set-up scenario would be that a site allows users to upload files to the site, say, images that the users might want to attach to forum posts they create. If there aren't security measures, and the files that the users are allowed to upload live in a web-... | https://security.stackexchange.com |
350,470 | [
"https://softwareengineering.stackexchange.com/questions/350470",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/63946/"
] | One of the common arguments for using microservices is better scalability. But I wonder whether this argument is really valid.
Lets say we had an application consisting of 10 microservice with 9 of them having each two instances (for redundancy) and one of them with 4 instances to handle the load (scalability). The p... | The point of microservices is not to reduce processor load. In fact, because of the overhead of communication and repetition of functions that used to be global utility code, it usually <em>increases</em> processor load somewhat.
The point of abolishing a monolith is much more to be able to maintain, deploy and run a ... | You are mostly correct. If you have quick services which are loaded equally you might as well install them all on all the boxes. It isn't as 'nice' as having a box per service, but it does save money.
However. as soon as you have an imbalance, say service 5 takes 100% of the cpu for 2min, you want to move that service... | https://softwareengineering.stackexchange.com |
2,099,410 | [
"https://math.stackexchange.com/questions/2099410",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/253787/"
] | I am trying to prove that this is false: $-m + n \geq |m + n|$ where m is a positive number and n is any number.
Can I subtract n from both sides? If not, how do I show that is false?
| Since $m$ is a positive number, we know that either $m+n\geq 0$ or $m+n<0$. Consider these two cases:
<ul>
<li>If $m+n\geq 0$, then $|m+n|=m+n$, so your inequality is equivalent to $-m+n\geq m+n$, subtracting $n$ from both sides gives $-m\geq m$, which is not true for a positive number.</li>
<li>If $m+n<0$, the... | Hint: Choose $m=n> 0$ and conclude
| https://math.stackexchange.com |
204,349 | [
"https://dba.stackexchange.com/questions/204349",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/149415/"
] | I'm doing a query with a join on two tables, where I need to do an ILIKE filter on a field in each of the tables with wildcards at both ends, and it should return a row if either of them match.
Approx:
<pre><code>SELECT * FROM "tableA" LEFT OUTER JOIN "tableB" ON
"tableA"."tableB_id" = "tableB"."id"
WHERE "tableA".... | It's sometimes useful to rewrite a query with <code>OR</code> conditions as a <code>UNION</code> (<code>ALL</code>) query. This usually leads to a different execution plan which may be more efficient. Testing will identify which of the two methods/plans is more efficient in each case (eg. if the trigram indexes are use... | It would be quite complicated to implement that type of optimization, and no one has done so yet. You couldn't do either just a nested loop from A to B, nor just one from B to A. You would have to have a nested loop in both directions with some mechanism to eliminate duplicates rows in the cases where both branches of ... | https://dba.stackexchange.com |
40,205 | [
"https://electronics.stackexchange.com/questions/40205",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/11121/"
] | I've heard and read about the passive sign convention, but don't really understand its meaning and importance in solving electric circuits. Is this because of conventional current which flows opposite electrons or is it something else?
| The passive sign convention is necessary to determine whether a circuit element is dissipating power, like a resistor, or providing power to the circuit. To calculate an element's power using P=VI you have to measure the voltage across the element. Suppose you use a voltmeter and you connect the red lead to one termina... | The "passive" in passive sign convention means that you are assigning positive voltage drops to passive components (i.e. loads). Negative voltage drops then occur across sources.
Why you ask? Why not positive voltage drops across sources and negative voltage drops across loads (i.e. active sign convention which you wi... | https://electronics.stackexchange.com |
624,239 | [
"https://electronics.stackexchange.com/questions/624239",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/20711/"
] | There are several techniques that can be used to transfer data between two asynchronous clock domains. For a few bits, and depending on direction of data between the two clock domains, one could use register chain for slow -> fast domain and use pulse stretching for fast -> slow. It is also possible to use handsh... | No.
If you move one bit into the other domain, and that bit is sufficiently slow (compared to both clock rates) then there is a chance that its value will be "incorrect" or unresolved for ONE clock cycle - e.g. due to the bit change hitting the tiny metastability window,
However even in that case, the NEXT cl... | It seems you've heard of metastability calculations. If so, you've probably noticed the part about a mean-time-between-failure dependence on four parameters (metastability resolution time, metastability time window, and clock and async data edge frequencies). You design your CDC synchronizers accommodating MTBF to be s... | https://electronics.stackexchange.com |
3,528 | [
"https://mathoverflow.net/questions/3528",
"https://mathoverflow.net",
"https://mathoverflow.net/users/1330/"
] | Let Σ be an axiom system. Can there be a formula φ, s.t.
<ul>
<li>Con(Σ) does not imply Con(Σ + φ) AND</li>
<li>Con(Σ) does not imply Con(Σ + not φ)</li>
</ul>
If yes, can you give me an example for ZFC?
| No, it's impossible for any axiom system. If Σ is consistent, then by the Completeness theorem, it has some model M. In M, φ is either true or false. So M is a model of either (Σ+φ) or (Σ+not φ). So at least one of them is consistent. It might be that your metatheory doesn't know which one... | Now that I know the answer, I've found my own simple proof. Probably it's interesting to someone else, so I post it:
I want to show that Con(Σ) is equivalent to ( Con(Σ + φ) OR Con(Σ + not φ) )
Proof:
Con(Σ + φ) OR Con(Σ + not φ) iff
( Σ doesn't prove [φ -> FALSE] ) OR
( Σ doesn't prove [not φ -> FALSE] ) iff... | https://mathoverflow.net |
57,598 | [
"https://mechanics.stackexchange.com/questions/57598",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/40490/"
] | I have a 2003 Corolla which was shaking pretty badly upon braking. I replaced the front rotors and brake pads—and everything went well. After a couple of days of driving, I began to hear a harsh grinding noise; it sounds like a low, raspy metal on metal grind. At first I thought it was coming from my passenger-side bra... | The problem <em>was</em>, in fact, the rear drum brakes. They were pretty worn down.
When I changed the front brakes, there was more pressure in the system (when I pushed onto the brake pedal) going to the rear brakes. This pushed the rear brakes into the drum harder than before I changed the front brakes, causing the... | If the noise IS actually eminating from the rear brakes its time to pull the drums off and check the brake shoe linnings.
If the handbrake was firmly applied when you were doing the front pads and the car was only jacked up at the front, then its possible that one of the rear shoe linnings has detached from it backin... | https://mechanics.stackexchange.com |
17,768 | [
"https://dba.stackexchange.com/questions/17768",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/4006/"
] | Requesting help with <strong>naming</strong> TSQL functions.
<h2>Existing function names (see below for table and relationship descriptions)</h2>
I currently have functions named as follows:
<ul>
<li><em><strong>CustomerYearsGetByYearRangeOffset</em></strong>: For each CustomerID, return <strong>all</strong> of the... | I think I identified the source of my confusion as well as several solutions:
<ul>
<li>My confusion seemed to stem from existing function names <em>implying</em> the fields used for grouping </li>
<li>For example, existing function <strong>ObjectRevisionIDsGetLatestByYearRangeOffset</strong> groups by <strong>ObjectID... | Where are these functions being called? Are they being called often? How complex is the logic, does it even warrant creating a new database object?
They are very verbose, and the new ones match that style so I guess they're ok. I would prefer to start with Get then I know right away its more of a 'getter' than a subro... | https://dba.stackexchange.com |
273,838 | [
"https://electronics.stackexchange.com/questions/273838",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/69481/"
] | Let's say I have very fine gauge wire of 0.005" (0.127 mm) diameter.
This wire is completely exposed (i.e. no insulation). What are available methods for terminating this to a PCB? Searching through Digikey and Mouser, the smallest gauge terminal blocks I could find were only 30AWG.
I'm thinking that there must be s... | No reason you can't use a standard header pin, or a wire wrap pin, wrap it around then solder.
Alternatively, a copper landing/square/point can be used.
Often small gauge wire is soldered to test points for debugging or hacking purposes, and that's essentially what you'd be doing.
| 0.127 millimeter isn't really all that unhandleable. Simply solder it on – a wire that small isn't something that you can exert reasonable force on, anyway, so any "plugging" where the wire might be exposed to mechanical forces isn't a good idea.
If you really needs something de- and reattachable: get a thicker wire (... | https://electronics.stackexchange.com |
201,159 | [
"https://physics.stackexchange.com/questions/201159",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/89191/"
] | all forms of energy can be stored or amplified for example : capacitor , hydraulics ,laser , pulley , etc..
what is the equivalent to that for magnetic force ?
can magnets be connected in series or parallel ?
| In the limit that $T\rightarrow\infty$, the partition function and the multiplicity of states are equal.
Why? Well, we have that $Q=\sum_{i} e^{-E_i/kT}$, where $i$ indexes all possible microstates. If $T\rightarrow\infty$, these Boltzman factors all approach one, and we have $Q=\sum_i 1=\Omega$.
You might think that... | <blockquote>
They look like they could be related. What is the relationship?
</blockquote>
From your two equations, we have
$$k\ln \Omega = k \ln Q + kT\frac{\partial}{\partial T} \ln Q = k \ln Q + \frac{kT}{Q}\frac{\partial}{\partial T}Q$$
but
$$Q = \sum_ie^{-\frac{E_i}{kT}}$$
and so
$$k\ln \Omega = k \ln Q + ... | https://physics.stackexchange.com |
346,885 | [
"https://softwareengineering.stackexchange.com/questions/346885",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/146935/"
] | When I retrieve data from database I name the class as <code>Model</code>, for example <code>UserModel</code>.
When I send data to the View I name the class as <code>ViewModel</code>, for example <code>UserSettingsViewModel</code>.
How to name the class that exchange data between layers?
| My suggestion is to omit the 'Model' suffix from your main class. I have seen 'DataTransport' or 'DT' classes, but generally you shouldnt need a separate class for this.
example classes
<ul>
<li>Database Table : User</li>
<li>read into : DataReader (from db client)</li>
<li>which populates : User</li>
<li>which popul... | A Gateway suffix is also used, for example DataAccessGateway between the DAL and the business logic layer is responsible to convert the data to a model object that is received by the business logic that works with a model of the data
| https://softwareengineering.stackexchange.com |
1,673,182 | [
"https://math.stackexchange.com/questions/1673182",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/318020/"
] | I have a water tank, a horizontally placed cylinder with two ends (one at right, the other at the left), these ends have a spherical cap [not hemispherical] of a sphere whose radius is $R$.
Given $L$, the level of water from ground (as in figure), and $W$, the width (i.e. the distance between the top of the spherical ... | Maple writes these solutions in various ways. In terms of Kummer M and U functions. Or in terms of Whittaker M and W functions. Or in terms of hypergeometric ${}_1F_1$ functions. Or in terms of Laguerre L functions.
So I'm guessing the solutions are usually not elementary functions.
| Did you try method of variation of parameters ?
| https://math.stackexchange.com |
112,680 | [
"https://softwareengineering.stackexchange.com/questions/112680",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/34339/"
] | When working on multiple projects simultaneously (for the sake of simplicity let's say half time each on two projects), which is better? Should the two projects
<ul>
<li>Use the same language? Same/similar frameworks?</li>
<li>Use entirely different languages?</li>
</ul>
Additionally, is it best if they are target fo... | First of all, the <strong>actual requirements should drive</strong> the decision behind what language, frameworks and tools to use.
If the requirements allow you to work on similar languages, frameworks and tools, then you should definitely try to keep things as consistent as possible.
You want to keep things simi... | You should strive to use the best tools for the job at hand. However, if the best tools' usage are utterly unknown to the developers these may not be the best tools.
| https://softwareengineering.stackexchange.com |
124,992 | [
"https://mathoverflow.net/questions/124992",
"https://mathoverflow.net",
"https://mathoverflow.net/users/8032/"
] | Let $X$ be a based space. Then the Moore loop space $MX$ is defined to be the topological monoid whose points are based loops $[0,a] \to X$ where $a \ge 0$ is allowed to vary. Composition is gotten by concatenating loops.
Since $MX$ is a topological monoid, we can form the <em>bar construction</em> $BMX$.
This is geo... | I wrote down two quick and simple solutions in Lemmas 14.3 and 15.4 on pages 84 and 90 of
"Classifying spaces and fibrations ([15] on my web page). The first is the evident zigzag
of natural weak equivalences
$$ X \leftarrow B(PX,MX,\ast) \rightarrow B(\ast,MX,\ast) = BMX, $$
where $PX$ is the Moore path space.... | I think the following will do, but it is not pretty.
Write an element of $\Delta^n$ as a tuple $0 \leq x_1 \leq \cdots \leq x_n \leq 1$. Identifying $[0,1]$ with $[-\infty, \infty]$, we may as well consider an element of $\Delta^n$ as a tuple $-\infty \leq x_1 \leq \cdots \leq x_n \leq \infty$.
Write a point $x$ in $... | https://mathoverflow.net |
3,220,742 | [
"https://math.stackexchange.com/questions/3220742",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/-1/"
] | Let <span class="math-container">$X$</span> be a topological space and <span class="math-container">$A\subset X$</span>, <span class="math-container">$$\overline{A}=\{x\in X \mid \forall U\text{ open with }x\in U,U\cap A\neq \emptyset\},$$</span> where <span class="math-container">$\overline{A}$</span> is the closure o... | Let <span class="math-container">$\theta = \sqrt[3]{2}$</span>. Then the conjugates of <span class="math-container">$\theta$</span> are <span class="math-container">$\theta\omega$</span> and <span class="math-container">$\theta\omega^2$</span>, where <span class="math-container">$\omega$</span> is a primitive cubic roo... | Divide <span class="math-container">$$(x^3+6x^2-2):(x-(\sqrt[3]{4}-\sqrt[3]{2}))=$$</span>
and you will get a quadratic one.
| https://math.stackexchange.com |
623,285 | [
"https://electronics.stackexchange.com/questions/623285",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/307230/"
] | I want a switching regulator (eg LM2596) set to 5v output voltage to work with 5V - 36V input voltage.
I know regulators have min dropout voltage. So how does it behave in such a case (Vin=5V when Vout=5V)?
What is the best practice of this application I want?
| It depends on the specific regulator.
Some buck regulators have 100% duty cycle mode. In that case, the top FET turns on, and it's just like having a resistor between Vin and Vout with a value equal to the RDSon of the FET.
Some buck regulators have a maximum duty cycle, (often so they can charge the bootstrap cap). ... | Depends on type. LM2596 for example, I believe can run up to 100% duty cycle, but has a Sziklai type output stage, so drops about a diode drop minimum, or about 5.8V minimum input (unless the control needs more; and certainly more at higher load current, hence the 7V recommended minimum input).
Most bootstrap (NPN/NMO... | https://electronics.stackexchange.com |
43,180 | [
"https://mathoverflow.net/questions/43180",
"https://mathoverflow.net",
"https://mathoverflow.net/users/10256/"
] | Hello,
I'm trying to bound an integral. I have a function $A(\nu) = | 1 + \exp(-I \nu) |$ (with $I$ being the imaginary unit) and I want to show that the condition (Paley-Wiener criterion for causality) applies
$$\int_{-\infty}^{\infty} \frac{|\log(A(\omega))|}{1+\omega^2} \mathrm{d}\omega < \infty$$
(log is the n... | You want to show that
$$\int_{-\pi}^\pi|\log|1+e^{-it}||dt$$
is finite. Now
$$|1+e^{-it}|=|e^{it/2}+e^{-it/2}|=2\cos(t/2)$$
so your integral is
$$\int_{-\pi}^\pi|\log|2\cos(t/2)||dt
=2\int_0^\pi|\log|2\cos(t/2)||dt.$$
Replacing $t$ by $\pi-2$ in the last integral gives
$$2\int_0^\pi|\log|2\sin(t/2)||dt.$$
The integrand... | The key is to understand the behavior of $A(\nu)$ near the singularity $\nu=0$. Using Taylor expansion we know that for $\nu$ small $A(\nu) = 1+e^{-I \nu} \approx -I\nu$. Therefore,
$\log|A(\nu)| \approx \log|-I \nu| = \log |\nu|$. Note that $\int_{-\pi}^\pi \log|\nu| d\nu = 2 \int_{0}^\pi \log \nu d\nu < \infty$. ... | https://mathoverflow.net |
53,312 | [
"https://security.stackexchange.com/questions/53312",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/41944/"
] | Should a user be allowed to request a password reset email and then log in (i.e. disregarding the reset email and using their existing password) or should the current account be locked until the password is reset?
If you disabled the account I could see this being abused by an 3rd party (i.e. requesting a password res... | As you say, you must allow the user to continue logging in otherwise this could be abused. If you locked them out effectively you are creating a Denial of Service vulnerability by letting an attacker deny service to a legitimate user.
I cannot see what is achieved by locking the user out. if you are preventing someone... | They should be allowed to log in after the email is sent.
After all clicking on the reset link in the email is what triggers the reset, not requesting the email. As you mention yourself, locking the account when asking for reset mail could lead to abuse.
| https://security.stackexchange.com |
64,513 | [
"https://stats.stackexchange.com/questions/64513",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/21030/"
] | I'm wondering if you could quickly advise on the best statistical analysis for my data.
I have a designed experiment with 12 plots within one larger area. This area was blocked into 6 to overcome issues of natural gradients present there, so there are 2 plots in each block.
Treatment 1 is a two level treatment split... | So I've done a lot of reading and chatting to people and I have a solution.
My experimental design is a split plot design, which is quite different from a nested or hierarchical design. I was originally confusing the terms. As Robert correctly states in his answer, what is needed is a mixed effects model. Thus:
... | My suggestion is to use a mixed effects model with
<ul>
<li><code>Treatment</code> 1 and 2 as factors (fixed effects)</li>
<li><code>Year</code> as an interval-scaled factor</li>
<li><code>Block</code> as a random factor</li>
</ul>
<blockquote>
Q: Should <code>year</code> be treated as a random effect?
</blockquote... | https://stats.stackexchange.com |
538,066 | [
"https://physics.stackexchange.com/questions/538066",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/257300/"
] | I have recently begun to learn QM and I cannot solve this task:
Let's say I have operator <span class="math-container">$\hat H = \begin{bmatrix}\epsilon & \upsilon \\ \upsilon & \epsilon \end{bmatrix} ,(\upsilon \in \mathbb{R} \backslash \{0\}) $</span> in a orthornormal basis defined by <span class="math-cont... | Yes, indeed, you simply need to calculate the matrix elements of the Hamiltonian in the new basis:
<span class="math-container">\begin{array}
\hat{H}_{11}' = \langle \phi_1'|\hat{H}|\phi_1'\rangle =
\frac{1}{2}(\langle\phi_1| + \langle\phi_2|)\hat{H}(|\phi_1\rangle + |\phi_2\rangle) = \\
\frac{1}{2}(\langle \phi_1|\ha... | The easy way in which you will always get there is just by diagonalizing the system first. When you "solve" a Hamiltonian you always search for the eigenvectors (=eigenstates) and eigenvalues. Let's try and do this for this Hamiltonian now first. We find the eigenvalues through the following characteristic equation:
<s... | https://physics.stackexchange.com |
569,504 | [
"https://electronics.stackexchange.com/questions/569504",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/42970/"
] | I've created an 8-bit VGA controller that outputs a 400x300 RGB signal. I also want to implement an AV output using PAL encoding. I don't understand how I can achieve the same resolution since the color subcarrier has a frequency of 4.43Mhz. Since the active video is 52μs long, I can only have 52x4.43 = 230 color pixel... | There are basically no pixels in an analog PAL (or NTSC) signal.
While the subcarrier is 4.43361875 MHz (or 3.579545 MHz for NTSC), the video information is still analog.
The color information just can't change as fast as the luma due to chroma being bandwidth limited to about 1.3 MHz in PAL (NTSC is different).
And th... | In PAL (and NTSC), the color information is deliberately bandlimited and undersampled in order to reduce the analog signal bandwidth requirements while maintaining "reasonable" picture quality. This is based partly on the fact that the human eye has greater spatial resolution for intensity than for color.
So ... | https://electronics.stackexchange.com |
448,724 | [
"https://physics.stackexchange.com/questions/448724",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/214901/"
] | Many people think of the water analogy to try to explain how electromagnetic energy is delivered to a device in a circuit. Using that analogy, in a DC circuit, one could imagine the power-consuming device is like a water wheel being pushed by the current.
In the case of an actual water wheel, the more water that flow... | Power to a water-wheel depends both on the current (amount of water delivered)
and the head (vertical drop of water as it turns the wheel). So, the
water analogy does have TWO variables that multiply together to make
power: current, measuring (for instance) the water flow at Niagara,
and vertical drop (like the heigh... | Here is a simple way to keep this stuff straight.
Power is always the product of an effort variable and a flow variable. In hydraulic systems, the effort variable is pressure and the flow variable is the flow rate.
For flow in open channels, the effort variable is typically very small (but not zero) and the flow va... | https://physics.stackexchange.com |
440,904 | [
"https://mathoverflow.net/questions/440904",
"https://mathoverflow.net",
"https://mathoverflow.net/users/78539/"
] | Let <span class="math-container">$\lambda_1\ge \ldots \ge \lambda_n \gt 0$</span>. Define a function <span class="math-container">$F:\mathbb R_+ \to \mathbb R_+$</span> by
<span class="math-container">$$
F(t) = t^2\sum_{i=1}^n\frac{\lambda_i^2}{(\lambda_i + t)^2}.
$$</span>
It is clear that <span class="math-container"... | It is immediate to show that
<span class="math-container">$S_1(x)=-x/24-\log(\eta(ix/(2\pi)))$</span>
and <span class="math-container">$T_1(x)=S_1(x)-2S_1(2x)$</span>, so all these formulas are immediate
consequences of the properties of the Dedekind <span class="math-container">$\eta$</span> function.
| <span class="math-container">$T_1(x)$</span> and <span class="math-container">$S_1(x)$</span> are related by <span class="math-container">$T_1(x)=S_1(x)-2S_1(2x)$</span>
Therefore,
<span class="math-container">$$S_1(2\pi)+T_1(2\pi)=\frac{\pi}{6}-\frac{3}{4}\log(2)$$</span>
is equivalent to
<span class="math-container">... | https://mathoverflow.net |
2,247 | [
"https://softwareengineering.stackexchange.com/questions/2247",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/666/"
] | How can I track that I'm developing software more or less productive than the previous days?
| There's a simple answer: you can't. And moreover, you shouldn't.
You want to measure your own productivity, but you can generalize: how can you measure productivity of programmers? First of all you have to define what you mean for "productivity": amount of code produced? Amount of design (or specification) implemented... | I'd say the best way to measure your productivity is to set a goal each day for what you want to have done that day, and if you complete it, consider it productive. It's a fairly subjective measure, but you'll most likely find it much more rewarding than an objective one.
| https://softwareengineering.stackexchange.com |
349,995 | [
"https://stats.stackexchange.com/questions/349995",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/109776/"
] | Say we have a polynomial kernel of degree two: $k(x,x')=\langle x,x' \rangle^2$ for $X=\mathbb{R}^2$. I know that a feature map $\phi(x)=(x_1^2,\sqrt{2}x_1x_2,x_2^2)$ exist. What I want to know is what is the corresponding RKHS?
| Non-probabilistic machine learning models <em>do not</em> handle uncertainty about the parameters. They simply return point estimates for the parameters. You may use additional techniques (e.g. bootstrap) to learn something about the uncertainty. Many of the available solutions (e.g. using dropout also at the predictio... | <h3>A note on definitions:</h3>
From your clarifying comment for examples of what you mean by "probabilistic":
<blockquote>
K-means (non-probabilistic) vs. Gaussian mixture model (probabilistic).
</blockquote>
It sounds like you're talking about what the literature usually calls parametric vs. non-parametric ... | https://stats.stackexchange.com |
438,303 | [
"https://electronics.stackexchange.com/questions/438303",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/212660/"
] | I'm attempting to copy and paste several components from one Altium PCB to another. I would like to copy and paste all the components all at once, because they are mounting hardware for another PCB, and their relative layout is crucial.
My problem is that when I select and copy all the components (a header, an outlin... | It literally stores lines of machine code from program memory (aka the entire instruction you line in your original post.
The fact you even discuss "storing all possible op codes in cache" points to a deeper misunderstanding. Talking about storing all possible op codes in cache (or any memory for that matter) has no m... | The Instruction cache stores the most recently used instructions and their addresses so that if an instruction needs to be repeated it doesn't have to be retrieved from main memory - this is much quicker.
For example the first time a loop is performed the instructions will be retrieved from main memory and simultaneou... | https://electronics.stackexchange.com |
176,585 | [
"https://mathoverflow.net/questions/176585",
"https://mathoverflow.net",
"https://mathoverflow.net/users/15242/"
] | <strong>Background/Setup</strong>
For any connected scheme $S$, let $\text{FEt}_S$ denote the category of finite etale $S$-schemes. Let $f : X\rightarrow Y$ be a morphism of connected schemes, then for any finite etale cover $C\rightarrow Y$, we can pull it back to a finite etale cover of $X$, so after making a choice... | (This was meant to be a comment elaborating on Dan Petersen's answer, but got too long.) The error is that you cooked up an isomorphism between $F_x \circ f^{\ast}$ and $F_x$ and <em>by means of that</em> simply declared the two functors to be "equal" yet never tried to calculate how this identification interacts with ... | The answer is that even though $C$ and $C \times_{X,f} X$ are equal as abstract schemes (with your definition of the fibered product), they are not equal as <em>schemes over $X$</em> - their structure morphism is different.
| https://mathoverflow.net |
471,132 | [
"https://physics.stackexchange.com/questions/471132",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/159990/"
] | <img src="https://i.stack.imgur.com/L2Ymo.jpg" alt="enter image description here">
I tried to solve a physics problem that involves a cylinder on a truck that is accelerating. I'm supposed to solve the acceleration of the center of mass of the cylinder when the acceleration of the truck, and the radius and the mass of... | The place to start on this problem is with the kinematics. Let v represent the velocity of the CM of the cylinder, and let <span class="math-container">$\omega$</span> represent the counterclockwise rate of rotation of the cylinder. Then the tangential velocity at the bottom of the cylinder is <span class="math-conta... | View the wheels of the truck as toothed gears and the ball or cylinder as a toothed gear. If the truck moves forward then the cylinder/gear will do what any gear would do on top of another...it has to move in the opposite direction.
| https://physics.stackexchange.com |
1,629,815 | [
"https://math.stackexchange.com/questions/1629815",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/32119/"
] | Let $k$ be an algebraically closed field and let $X$ be a non-singular algebraic projective curve over $k$. Very often, when most books present the function field $k(X)$, they say that "it is the analogue of the field of meromorphic functions on a Riemann surface". I don't agree with this statement, and I'm going to e... | I don't follow your reasoning. The classical sense in which $k(X)$ is analogous to meromorphic functions on a Riemann surface is that when $k = \mathbb{C}$ it is <em>literally</em> meromorphic functions on a Riemann surface. The completion you describe is completely different: it's a completion of germs of meromorphic ... | Locally a meromorphic function is a quotient of holomorphic functions. I guess that's where the analogy comes from.
| https://math.stackexchange.com |
63,383 | [
"https://cs.stackexchange.com/questions/63383",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/58211/"
] | As a starting point for our course in Artificial Intelligence, we are being taught induction. We received a number of homework assignments where we have to show our inductive approach for a given problem.
An example of such a problem: "Sort an array of N numbers".
Reading through the course material and online source... | It seems to me that your teacher wants a induction proof where the induction is on the length of the array. It seems weird that your teacher does not provide a sorting algorithm .
If the task is to sort an array, I would assume that your teacher is looking for an, as you say, arbitrary sorting algorithm and prove it w... | Most questions in AI textbooks of this style are intended to be open ended so that the student can experiment on its own with the problem. So the golden rule is do as you see fit to provide the best learning!
In particular for this problem, your approach seems appropriate.
Since most sorting algorithms fall into a di... | https://cs.stackexchange.com |
118,336 | [
"https://security.stackexchange.com/questions/118336",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/98440/"
] | Is that possible to trace the actions performed by a virus? Run Time , stolen data and the files consulted and get the relative impact on my pc.?
| <strong>I strongly recommend</strong> to run that virus in an artificial environment like a sandbox so you won't affect your personal computer! In this way you can track its activity through the sandbox specific CLI/GUI.
Sandbox Example: Cuckoo Sandbox, Sandboxie, etc.
<strong>The other way around:</strong>
Use an ... | After the facts? Very unlikely unless you have full egress logging and remote audit files of the system that was compromised and even then it's not 100% reliable.
If you want to know what a Virus does there's always malware analyzers like Cuckoo.
| https://security.stackexchange.com |
64,105 | [
"https://cs.stackexchange.com/questions/64105",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/53213/"
] | I realized that almost no one explained how to selected the type variable T1
<pre><code> Γ ⊢ e1 : T1 -> T , Γ ⊢ e2 : T1
-------------------------------- T-APP
Γ ⊢ e1 e2 : T
</code></pre>
when doing type checking (from bottom to top).
So, the question is how T1 is introduced? Is there any condition about T1?
| "T1" is obtained from typing context by doing derivation on the right branch of application rule. I worked on some type checking examples and concluded that.
| It depends on what the expression <code>e2</code> (and <code>e1</code>) is and what other type rules are in the type system.
Basically, the <code>Γ ⊢ e2 : T1</code> part of the type rule says:
<blockquote>
If there is a rule in the type system, which assigns the type <code>T1</code> to the expression <code>e2</code... | https://cs.stackexchange.com |
140,224 | [
"https://electronics.stackexchange.com/questions/140224",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/53708/"
] | I just wrote a program to use in PIC16F72. I was trying to simulate it on Proteus and I found that Proteus doesn't have that microcontroller in its library. I read somewhere that PIC16F72 and PIC16C72 are almost the same. So does that mean I can write a program for C72 and use it on F72?
| The two chips are <em>almost</em> the same. They use the same instruction set, so yes, you can execute a program written for C72 on F72.
However, there are differences, some of which could be critical:
<ul>
<li>The C72 lacks the ability to read the program memory as data.</li>
<li>The C72 is an OTP (One-Time Program... | The F72 is the modern version with flash based program memory. The C72 is an older, one time programmable version. As far as simulation goes, they are identical, but for debugging hardware, you would want the F72 to be able to erase and reprogram.
| https://electronics.stackexchange.com |
645,424 | [
"https://physics.stackexchange.com/questions/645424",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/36793/"
] | In the Langevin model, if we make the assumption that the random force <span class="math-container">$\eta(t)$</span> acting on the Brownian particle is a stationary, Markovian, and gaussian process, does it automatically ensure that the autocorrelator <span class="math-container">$\langle\eta(t_1)\eta(t_2)\rangle\propt... | Delta-correlated process and Markovian process is not necessarily the same thing (although the terminology may vary - my discussion is based on the theory of random processes, but, e.g., in the theory of master equations <em>Markovian</em> is understood somewhat differently).
<strong>Markovian process</strong><br />
Ma... | To answer your first question,
<blockquote>
In the Langevin model, if we make the assumption that the random force
η(t) acting on the Brownian particle is a stationary, Markovian, and
gaussian process, does it automatically ensure that the autocorrelator
<span class="math-container">$⟨η(t_1)η(t_2)⟩∝δ(t_1−t_2)$</span>?
... | https://physics.stackexchange.com |
20,444 | [
"https://math.stackexchange.com/questions/20444",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/1069/"
] | If I'm given a curve as an implicit function, is there some algorithm for obtaining a parametrization of the curve?
For example, how would I parameterize
$\frac{2x}{y} - \frac{3y}{x} = 8$
I know I might use $\cosh$ and $\sinh$, but I'm wondering if there's a surefire way to parameterize a curve, when you have a form... | Quoting Arturo Magidin:
<blockquote>
There is no general algorithm that will always yield a good parametrization of any curve. Relatively simple trigonometric parametrizations cannot work in general, because they always yield closed curves (being periodic). Parametrizing curves generally takes ingenuity, not unthinkin... | Solve a quadratic equation for $y$.
| https://math.stackexchange.com |
57,546 | [
"https://stats.stackexchange.com/questions/57546",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/24998/"
] | I have a set of cities ranked 1-10 based on several criteria. I also have the percentage of the total population living in these cities. I want the cities with smaller populations to be able to compete with larger cities, so I want to give the population percentages a weight that will compensate for smaller population ... | It's still not perfectly clear exactly what your methods are, but you can <strong>normalize</strong> on city population. Say B (for big) has 200 stores and 100,000 people while S (for small) has 14 stores and 10,000 people. A simple normalization is to divide store count by population size. focus(B) = 200 / 100,000 and... | One would usually weight according to population size to give smaller cities less importance. In your case you don't want to give them less importance.
So don't weight your values.
If you don't put any weights into the aggregates you're computing, that is effectively treating them equally.
Did I understand your ques... | https://stats.stackexchange.com |
477,720 | [
"https://stats.stackexchange.com/questions/477720",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/291651/"
] | I vaguely recall a definition of a pseudorandom generator from cryptography. My rephrasing here:
No adversary can (with non negligible probability) predict the next bit of a uniformly (pseudo)random sequence of bits with accuracy substantially greater than 50%
I define two number generators as follows:
<strong>A</stro... | A) Binomial. 40 or fewer errors out of 100 can be computed exactly in R as follows:
<pre><code>pbinom(40, 100, .5)
[1] 0.02844397
</code></pre>
B) Then one approach is to say that I have a random permutation of fifty <span class="math-container">$0$</span>'s and fifty <span class="math-container">$1$</span>'s. And, ind... | In option A, as BruceET says, any strategy by the guesser will lead to the same binomial distribution. In particular the expected number of correct bit guesses will be <span class="math-container">$50$</span>, and the probability of <span class="math-container">$60$</span> or more correct guesses will be <span class="... | https://stats.stackexchange.com |
90,882 | [
"https://electronics.stackexchange.com/questions/90882",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/27975/"
] | Why doesn't the Inductance/Capacitance of Laptop charging wires and other appliances effect the performance of the devices/ power supplies?
An inductance would be introduced if the wires are lying in a loop or mixed together.
| There will be a small inductance created by wrapping up a cord in a loop, but the effect will be negligible. There are two reasons for this. First, the inductance will be so small that the effect at power line frequency is negligible. Second, power cords carry both the supply and return so the overall current flowin... | Although this question is answered I'd like to say one thing but first the question: -
<blockquote>
Why doesn't the Inductance/Capacitance of Laptop charging wires and other appliances effect the performance of the devices/ power supplies?
</blockquote>
For many switch mode power supplies, the inductance and capaci... | https://electronics.stackexchange.com |
28,093 | [
"https://physics.stackexchange.com/questions/28093",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/9126/"
] | Is there any equation that states the relation between pressure and water flow.
I.e. Let's say that in 1 hour with 8mca (water collum meters) pressure I obtain 50m3. What if (giving the same contditions) I execute the same test but now with 15mca?
Is that just proportional?
| The water velocity into a region with atmospheric pressure goes as the square root of the pressure difference by Bernoulli's law. So if you quadruple the pressure difference, you get twice the speed.
This is not exact, because as the water fills up your container, unless it is coming from the very top, the building up... | All what Ron explained/wrote can be extracted directly from <strong>Bernoulli equation</strong>
$$\frac{1}{2} \rho v_1^2 + \rho g h_1 + p_1 = \frac{1}{2} \rho v_2^2 + \rho g h_2 + p_2.$$
Say, if you have the huge open container with small hole at the bottom, you have the same (atmospheric) pressure on the both ends $... | https://physics.stackexchange.com |
505,215 | [
"https://stats.stackexchange.com/questions/505215",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/308450/"
] | I have two sets of P-values. Each set contains about 1500 P-values that are computed by different versions -i.e. slightly different algorithms- of the same software. These two versions used the same input data and the P-values have the same meaning, but are slightly different. The algorithms test for an enrichment of c... | I won't demonstrate any more than you already know, but this approach might help confirm your suspicion that the parameter <span class="math-container">$k=1$</span> is special. Along the way you might find some useful general shortcuts.
<hr />
Let's begin far more generally: suppose only that <span class="math-contain... | You are correct that <span class="math-container">$\mathsf{Gamma}(\mathrm{shape}=1,\mathrm{scale}=\theta)$</span> is exponential, specifically <span class="math-container">$\mathsf{Expm}(\mathrm{mean}=\theta)\equiv\mathsf{Exp}(\mathrm{rate}=1/\theta).$</span>
Using the CDF method, you can show that if
<span class="math... | https://stats.stackexchange.com |
24,913 | [
"https://scicomp.stackexchange.com/questions/24913",
"https://scicomp.stackexchange.com",
"https://scicomp.stackexchange.com/users/21580/"
] | What would be the rigorous mathematical expression of the fact that a conservation law discretized with a Finite Element method with Galerkin discretization does not result in a conservative scheme ?
| Most pdes coming from physics have a divergence structure
$$
u_t + \nabla\cdot F =0 \qquad \textrm{in} \quad \Omega
$$
Then for any arbitrary control volume $D \subset \Omega$, we have
$$
\frac{d}{dt}\int_D u dx + \oint_{\partial D} F \cdot n ds = 0
$$
i.e., the total quantity inside $D$ changes due to fluxes on th... | A mathematical expression which shows that a scheme is not conservative is usually an inequality. For example, many methods for the Advection Equation (and generalizations) do not conserve energy (this is known as numerical dissipation). This is usually shown in a theorem like:
For $u_n$ being the approximation of $u(... | https://scicomp.stackexchange.com |
722,403 | [
"https://physics.stackexchange.com/questions/722403",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/321026/"
] | Based on the Maxwell equations we know that
<blockquote>
A time-varying magnetic field induces an electric field
</blockquote>
<blockquote>
A time-varying electric field induces a magnetic field
</blockquote>
Suppose that an electric field, which is induced by a time-varying magnetic field, is itself time-varying (not ... | You are thinking about it in the wrong way. What Maxwell's equations tell you is that when you have a time-varying magnetic field, there must also be an electric field present that satisfies the Maxwell-Faraday equation. The two fields co-exist (and indeed are different aspects of THE electromagnetic field). Similarly,... | Maxwell was being unnecessarily pedantic. The only way an electromagnetic field <em>can</em> vary is with time. <em>Any</em> field can only vary over time. So he was really only describing a simple variation of the field.
A variation of the <em>electromagnetic</em> field necessarily implies a variation in both its elec... | https://physics.stackexchange.com |
407,818 | [
"https://physics.stackexchange.com/questions/407818",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/196340/"
] | In my textbook, it is given that internal resistance of a car battery increases with decreasing temperature. But car batteries contain lead, which is a metal, and hence the resistance should decrease. Where am I wrong?
| If the battery only contained lead, you might be on to something. However, batteries are made with both metals AND something to transport the charges, called an "electrolyte". This is normally a liquid, and liquids have less <em>motility</em> as they get colder. This <em>motility</em> refers to the speed with which som... | Chemomechanics is right. Inside a battery, the dominant contribution to the internal resistance is not the lead plates but the powerful acid solution the lead plates are immersed in, and the boundary layer between the acid and the lead surfaces. Those resistivity effects are driven by chemical kinetics, most of which a... | https://physics.stackexchange.com |
348,295 | [
"https://softwareengineering.stackexchange.com/questions/348295",
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"https://softwareengineering.stackexchange.com/users/236972/"
] | I have been tasked with writing unit tests for an existing application. After finishing my first file, I have 717 lines of test code for 419 lines of original code.
Is this ratio going to become unmanageable as we increase our code coverage?
My understanding of unit testing was to test each method in the class to en... | Yes, with 100% coverage you will write some tests you don't need. Unfortunately, the only reliable way to determine which tests you don't need is to write all of them, then wait 10 years or so to see which ones never failed.
Maintaining a lot of tests is not usually problematic. Many teams have automated integration... | If you have worked on large code bases created using Test Driven Development, you would already know there can be such a thing as too many unit tests. In some cases, most of the development effort consists of updating low-quality tests that would be best implemented as invariant, precondition, and postcondition checks ... | https://softwareengineering.stackexchange.com |
492 | [
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"https://quant.stackexchange.com/users/42/"
] | I am currently developing a commercial automated trading program in which users can write their own proprietary code and develop strategies, like in NinjaTrader, MetaTrader etc. Right now I am working on the order handling part, which is really important. I can not figure out how to reference the orders entered during ... | Regarding your order management issue, every order should have a unique identifier that the user can reference; in FIX, this is the ClOrdID. The parameters of every order the user requests should be stored in a table keyed by this identifier.
If your goal is to prevent duplicate orders from going out, consider having ... | What I've done in the past is create an OnOrderSubmit event/method that fires when an order is placed. Use set a semaphore in that method so that your tick/analytical method ignores order placement instructions until an execution occurs or a timer expires. Then flip the semaphore.
(If you're using multiple threads yo... | https://quant.stackexchange.com |
135,705 | [
"https://chemistry.stackexchange.com/questions/135705",
"https://chemistry.stackexchange.com",
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] | <h3>Problem</h3>
<blockquote>
When the number of electrons in bonding molecular orbitals is equal to number of electrons in anti-bonding molecular orbitals bond cannot be formed between two atoms because
<strong>A</strong>) Bonding effect by the electrons in bonding M.O.s is cancelled by the antibonding effect of elect... | Choices B and C are two different ways of saying the same thing. Say <span class="math-container">$E_{MO}(A)$</span> and <span class="math-container">$E_{MO}(AB)$</span> are the energies of electrons in bonding and anti-bonding orbitals, respectively, relative to the electrons in the original atomic orbitals from which... | When a test question is so vague that you can't figure out what answer is best, it's difficult to formulate a question about the answers to the question. The test question specifies bonding electrons equal to antibonding electrons. No energy statements. There needs to be one more answer:
E. All of the above, although s... | https://chemistry.stackexchange.com |
44,596 | [
"https://mathoverflow.net/questions/44596",
"https://mathoverflow.net",
"https://mathoverflow.net/users/2625/"
] | The definition of a (geometric) vector bundle over a scheme $X$ can be rewritten as follows in terms of 'not-so-geometrical algebra' if $X=Spec R$ is affine and if I am not missing something.
A <em>vector bundle</em> of rank $n$ over $R$ is an $R$-algebra $A$ such that
<ul>
<li>for every $p\in Spec R$ there is a isom... | Given any $R$-module $M$, there is a scheme which corresponds to the 'total space' of $M$, given by
$$ Tot(M):=Spec( Sym_R(M*))$$
where $M*$ is the dual module $Hom_R(M,R)$ and $Sym_RM*$ is the symmetric algebra of $M^*$ over $R$. If $M$ happens to a free rank $n$ $R$-module, then $Sym_RM\simeq R[X_1,...,X_n]$. The ... | It may make more sense to look at the isomorphism class of a vector bundle as its corresponding isomorphism class as a locally free sheaf (Hartshorne: Algebraic Geometry - Exercise 5.18)
Then, it becomes clearer to see the connection by looking at the sheaf associated to a projective module $M$ - which is a locally fr... | https://mathoverflow.net |
17,523 | [
"https://bioinformatics.stackexchange.com/questions/17523",
"https://bioinformatics.stackexchange.com",
"https://bioinformatics.stackexchange.com/users/12859/"
] | So I have a file, let's call it pcawg.tsv. It's formatted like the one down below.
<pre><code>Tumor sample ID Normal sample ID Mechanism
a 1 deletion
b 2 ecDNA
c 3 ecDNA
</code></pre>
I have a file of tumor sample ID's with t... | This may help:
<pre><code>cat ecDNA_samples.tsv | xargs -I % grep '^%\s' pcawg.tsv
</code></pre>
The command above executes <code>grep '^<line>\s' pcawg.tsv</code>, for each line of ecDNA_samples.tsv. Which matches the lines taken from ecDNA_samples.tsv to the sequences of characters between line start and a whit... | Just in case an R solution is acceptable as well, this should be fairly robust code because it properly parses the TSV files and matches up column names:
<pre><code>#!/usr/bin/env Rscript
library(tidyverse)
read_tsv("pcawg.tsv") %>%
inner_join(read_tsv("ecDNA_samples.tsv")) %>%
write_ts... | https://bioinformatics.stackexchange.com |
83,746 | [
"https://stats.stackexchange.com/questions/83746",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/38176/"
] | OK, I know its not possible because Log(0) is undefined. But here is my Problem:
I measured a Weight gain of my Test object's over Time. Test objects, made of nonwoven material, were placed in very humid Atmosphere (enclosed above a Tank of heated Water). As they absorbed kondensated Water their total Weight would inc... | You've only got five points & a straight line looks like a good enough fit over their range. You say that points 3 & 4 should be higher owing to a defect of the measurement procedure but not why the other points shouldn't be higher by the same reasoning. So I'm not sure why you want to fit $\log w$ to $t$ (or t... | Why do you want to take the logarithm of the x-axis? If one observes data over time that seems to behave exponentially, one takes the logarithm of the observed data. So, I suggest you take the logarithm of the weights and plot this against time. Then you can just click on the plotted line of the graph, click on the lin... | https://stats.stackexchange.com |
3,031,340 | [
"https://math.stackexchange.com/questions/3031340",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/624281/"
] | Given equations of the form:
<span class="math-container">$A(r) = \int_{t_{1}}^{t_{2}}F(r,t)dt$</span>
<span class="math-container">$B(t) = \int_a^b F(r,t)r^2dr$</span>
where <span class="math-container">$A(r)$</span>, <span class="math-container">$B(t)$</span>, and all of the limits on the integrals are known, is ... | Let's look at the problem
<span class="math-container">$$
A(r) = \int_{t_{1}}^{t_{2}}F(r,t)dt\\
B(t) = \int_a^b F(r,t)r^2dr
$$</span>
in the particular case where <span class="math-container">$t_1 = -1, t_2 = 1, a = -1, b = 1$</span>.
Then if <span class="math-container">$F$</span> is any odd function, (odd in <span ... | What I would do is to find
<span class="math-container">$$A(r,t) = \int_{t_1}^t F(r,t) dt$$</span>
so that
<span class="math-container">$$A'_t(r,t) = F(r,t)$$</span>
Hence,
<span class="math-container">$$A'_t(r,t_1)=F(r,t_1), \ A'_t(r,t_2)=F(r,t_2), \ A'_t(r,t_3)=F(r,t_3), \dots$$</span>
which means you should be able ... | https://math.stackexchange.com |
1,305 | [
"https://physics.stackexchange.com/questions/1305",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/635/"
] | I've simplified this down by quite a lot but as far as I understand it, magnetic fields on the Sun's surface twist together and when it gets all a bit too much they release energy.<br>
My question is why can't we twist magnetic fields here on Earth to produce energy?
| We have conservation of energy to contend with. The magnetic energy being released in the upper layers of the suns atmosphere originated in turbulent convection lower down. So in effect the upper layers of the sun (upper here meaning roughly from the photosphere and downward) are acting as a heat engine putting some en... | If we could build a type of deep cycle battery system and attach them to our power lines, we could syphone off cme emissions, as for magnetic fields we us that energy to spin terbines , if we construck sails to collect solr winds , we could use that energy to fuel our international space station. What we realy need to ... | https://physics.stackexchange.com |
597,978 | [
"https://physics.stackexchange.com/questions/597978",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/281379/"
] | <span class="math-container">$I(x) = I_0 \cdot e^{~-u \cdot x}$</span>
Where u is the linear attenuation coefficient
And how does this relate to the following
<span class="math-container">$N(x) = N_0 \cdot e^{~-u \cdot x}$</span>
Where N is the count rate of the beam typically measured by a GM counter.
| That simplified form of continuity equation assumes that the fluid is incompressible. That is only a valid assumption at low Mach numbers. I think a typical “rule of thumb” is that a Mach number less than 0.3 is required for the assumption to hold. So for the continuity equation to hold in that form requires a speed wh... | You can check your hypothesis by closing the mouth of a pipe (from which water is flowing out) to different degrees. You will find that the flow velocity increases initially as the outlet area is decreased, reaches a maximum and then falls off to zero as you proceed to completely close the outlet. This is because, when... | https://physics.stackexchange.com |
479,693 | [
"https://physics.stackexchange.com/questions/479693",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/231829/"
] | Say we have an object with velocity in earth's frame that accelerates quickly.
For example, suppose we have some object that accelerates very quickly, and has speed <span class="math-container">$v$</span> in earth's frame of the form
<span class="math-container">$v(t)=c\sqrt{1-e^{-2t}}$</span>.
Then the proper time... | It is true that the condition for thermodynamic equilibrium between two systems in contact through a diathermal, rigid and impermeable wall is the equality of temperatures. This is a consequence of the principle of maximum entropy applied to the isolated system made of the two systems at thermal contact. Thermodynami... | <strong><em>I just read that "a heat transfer between a reservoir and a system at same temperature is a reversible process". If there's no temperature difference, why would there be a heat flow?</em></strong>
You are correct. If there is no temperature difference there can be no energy transfer in the form of heat. He... | https://physics.stackexchange.com |
33,020 | [
"https://electronics.stackexchange.com/questions/33020",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/7057/"
] | Would one large wind turbine be more efficient than many small wind turbines in theory?
| <blockquote>
Would one large wind turbine be more efficient than many small wind turbines in theory?
</blockquote>
The proper answer to this would take several days to write and would cost you money.Please advise if you wish to proceed :-).
However, the answer is "no", BUT there are factors that could bias the resu... | If the turbines were small, they would have less mass and hence would require less wind energy to spin. So the same wind force striking a large and small turbine would cause the small turbine to turn faster. A faster spinning turbine cause a larger current to be induced in the generator. This is assuming we could build... | https://electronics.stackexchange.com |
10,559 | [
"https://computergraphics.stackexchange.com/questions/10559",
"https://computergraphics.stackexchange.com",
"https://computergraphics.stackexchange.com/users/15572/"
] | I have a Dell monitor with 60 Hz refresh rate and therefore games playing on it are not very smooth as compared to 120 hz.
But when I open videos on YouTube of the same game on the same monitor, some of those videos run extremely smoothly as if it's a 120hz display.
Why is that so ?
| As you have now mentionned that your computer can actually keep up (at 150 fps no less), I suspect you have a case of temporal aliasing.
The problem is that 150 is not a multiple of 60. Let's say we look at one tenth of a second. That's 15 frames generated by your computer but only 6 can be shown on your screen. The fr... | Humans don't really see anything beyond 20-25 fps. Even less is often sufficient; animation at 12 frames a second work quite well too. So when you watch TV, the fps of your image is 25-30, and yet you don't generally accuse of them being not smooth.
Why do games require more? Well, because they are fast paced. There i... | https://computergraphics.stackexchange.com |
40,333 | [
"https://mechanics.stackexchange.com/questions/40333",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/16810/"
] | My car is an Audi S5 which has the normal cruise control (non-adaptive) with auto braking (applies brakes when going downhill too fast).
For some reason when engine braking the car uses around 4L/100KM instantaneous petrol. If I disengage cruise control, it will use 0L/100KM as it shuts off fuel. Therefore, I prefer t... | The cruise control on a modern car is totally electronic – obviously it has to interact with the car's controls, but no more so than would happen in "manual" driving. There should be no reason why you can't turn it on or off at will.
| I have VW Golf, which technologically should be similar to Audi, and I observe the same behavior you describe. I think the reason to keep the fuel on is that ECU can keep the speed constant in more cases, than with fuel shut off. Also with cruise control it seems to consume more fuel when you have many uphill/downhills... | https://mechanics.stackexchange.com |
518,809 | [
"https://physics.stackexchange.com/questions/518809",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/244231/"
] | I’ve been trying to work out if this is to do with electron avalanches caused by the ionisation of the gas in the chamber but can’t find much more online than “the detector needs time to reset”
| <strong>TL;DR -- dead time comes from resetting the detector, not doing this will cause a runaway process.</strong>
As a quick recap of the way a Geiger-Muller counter works:
<ol>
<li>Radiation enters the chamber, which is filled with a neutral gas (usually He, or Ar).</li>
<li>The radiation ionizes gas particles, k... | It's because of what's left over after the avalanche. You have electrons crashing into atoms, freeing more electrons, smashing into the anode, shooting out photons which trigger more cascades, until the whole tube lights up (you can see it in the dark if the coating on your mica window is flaking off). That's in contra... | https://physics.stackexchange.com |
143,813 | [
"https://mathoverflow.net/questions/143813",
"https://mathoverflow.net",
"https://mathoverflow.net/users/6756/"
] | Let $N(T)$ be the number of complex zeros of $\zeta(s)$ with imaginary part between $0$ and $T$, and let $N_k(T)$ be the analogous counting function for the $k$th derivative $\zeta^{(k)}(s)$. Based on numerical evidence for $T<100$, Spira conjectured in 1965 ("Zero free regions of $\zeta^{(k)}(s)$, J. London. Math.... | I'm looking at the review, by Haseo Ki, of Hirotaka Akatsuka, Conditional estimates for error terms related to the distribution of zeros of $\zeta'(s)$, J. Number Theory 132 (2012), no. 10, 2242–2257, MR2944752. It says,
Assuming the Riemann hypothesis, the author shows $$N(T)=N_1(T)+{T\log2\over2\pi}+O\left({\log T\... | Shorokhodov gave an explicit counterexample to Spira's conjecture in "Pade approximates and numerical analysis of the Riemann zeta function", Computational Mathematics and Mathematical Physics, vol. 43 no. 9 (2003) pp. 1277-1298. He computed, for <span class="math-container">$T=1420$</span>, 1000 zeros of <s... | https://mathoverflow.net |
148,859 | [
"https://electronics.stackexchange.com/questions/148859",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/5778/"
] | I'm trying to connect multiple components (same components) to an FPGA output. The FPGA runs at 30Mhz and transmitting both a clock and data on lines connected to these similar components.
Each component is located in a different distance from the FPGA where the shortest is 10mm and the longest is 300mm
<ol>
<li>When... | <blockquote>
<ul>
<li>When the difference is 290mm and the frequency is 30Mhz, do I need to worry about one signal reaching before the other?</li>
<li>Is there a rule of thumb or a way to calculate what is the maximum difference in distances that is allowed for a specific signal frequency?</li>
</ul>
</blockquo... | Follow The Photon's good advice, but I'll also add:
<ul>
<li>Use series termination resistors at the end of each stub closest to the slave device. Recommended value is typically 22-100R.</li>
<li>Have a read of the relevant configuration instructions for your FPGA; Xilinx (for example) goes into great detail about ho... | https://electronics.stackexchange.com |
166,942 | [
"https://physics.stackexchange.com/questions/166942",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/71374/"
] | I'm currently studying forces in physics and in this example, it states that <em>Fn +Fay = mg</em>. Why is this so? Is it because they are both in the same direction?
<img src="https://i.stack.imgur.com/pXAPm.png" alt="enter image description here">
<img src="https://i.stack.imgur.com/hmNMF.png" alt="enter image des... | That equation expresses the fact that the forces on the block in the vertical direction add up to zero. $F_n$ and $F_{ay}$ are both forces pulling the block upwards, while the force of gravity on the block is $mg$ downwards. We don't want the block to accelerate up or down, and so the net forces in the vertical directi... | Fn is the normal reaction force and Fay is the y-component of the force Fa, since the block is not moving in the y-direction (+ve or -ve) and since we know that mg is acting downwards, there has to be some force(s) balancing out mg, and apart from the normal reaction, Fay is also acting upwards, so yea it's Fn + Fay = ... | https://physics.stackexchange.com |
32,911 | [
"https://mathoverflow.net/questions/32911",
"https://mathoverflow.net",
"https://mathoverflow.net/users/5196/"
] | An important invariant of a knot in $S^3$ is its <em>Alexander polynomial</em>, related also to <em>Reidemeister torsion</em>. Is there something like that for knotted surfaces in $S^4$? If not, what are the difficulties?
| Yes for $S^2$, and more generally, depending on what you are after.
Given any torsion module $M$ over the PID $Q[t,t^{-1}]$, the order of $M$ is well defined in
$Q[t, t^{-1}]$ up to units, in the usual way. Moreover $M\otimes Q(t)=0$. These two facts are at the heart of why the Alexander polynomial is related to Re... | The ideals that define the homology of the infinite cyclic covering are not principal. So the Alexander polynomial, as a single polynomial, is not defined. Fox's example 12 from "A quick trick in knot theory" is the 2-twist spun trefoil. The ideal is generated by a pair of polynomials. I haven't thought about Reidemei... | https://mathoverflow.net |
43,790 | [
"https://security.stackexchange.com/questions/43790",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/31941/"
] | Can Biba model always be combined with Bell-LaPadula model? What are the issues that arise?Would there be conflicts?How would information flow be affected?
| To answer all your questions at once, since the BLP is <em>no read up, no write down</em> data confidentiality model, and Biba is <em>no read down, no write up</em> data integrity model, you effectively end up with a prohibitive, same level only data confidentiality and integrity model. In theory, it shouldn't result i... | The two deal with different subjects, so they can't use the same levels and categories. In effect, they're orthogonal. <A HREF="http://www.cl.cam.ac.uk/~rja14/book.html" rel="nofollow">[Anderson]</A>
However, both are exceedingly simple-minded and narrow, and can be a pain to syadmin.
--dave
| https://security.stackexchange.com |
3,306 | [
"https://physics.stackexchange.com/questions/3306",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/552/"
] | Consider two long wire with negligible resistance closed at one end of the resistance R (say a light bulb), and the other end connected to a battery (DC voltage). Cross-sectional radius of each wire is in <span class="math-container">$x = 100$</span> times smaller than the distance between the axes of the wires.
Quest... | The magnetic force should be straightforward, you probably have a formula for it, or you can use the field strength from one wire, cross the current in the other to compute the force.
The charge is more difficult, there you have two oppositely charged cyllinders separated by a distance. You can need to figure out the v... | I wrestled with this problem more than a week and got quite an unexpected result, i think. I am using SI system.
A starting point is that there are excessive surface charges at each of the wires, flows a current through them or not. Therefore, besides the magnetic force $F_m$ it is necessary to take into account als... | https://physics.stackexchange.com |
203,320 | [
"https://math.stackexchange.com/questions/203320",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/8917/"
] | If
$$U = \{(u,v)\mid 0 < u,\; 0 < v < 2\pi\},
$$
and
$$
x(u,v) = (u\cos v,u \sin v,u+v).
$$
Then how can we show that $x$ is a simple surface?
Is it necessary true that for being simple implies that we need:
smoothness
1-1
and class C^k or is there anything I have overlooked?
For being simple, we need t... | We can see that $x(u,v)$ is smooth, because $u, v, \cos v$, and $\sin v$ are all smooth functions.
To see that $x(u,v)$ is one-to-one, suppose $u,u,>0$ and $0<v,v'<2\pi$ such that
$x(u,v)=x(u',v,)$. This implies by definition that
$$(u\cos v,u \sin v,u+v)=(u'\cos v',u' \sin v',u'+v')$$
or equivalently,
$$... | For showing $1$-$1$. Try to think of an inverse of $x(u,v)$.
HINT: $\cos(v)^2+\sin(v)^2=1$
| https://math.stackexchange.com |
98,229 | [
"https://mathoverflow.net/questions/98229",
"https://mathoverflow.net",
"https://mathoverflow.net/users/288/"
] | In other words:
<blockquote>
What is $\mathrm{Ext}_{\mathcal{A}}^{4,t}(\mathbb{Z}/2,\mathbb{Z}/2)$?
</blockquote>
If the 4-line is not known, how much is known about it?
Here, $\mathcal{A}$ is the 2-primary Steenrod algebra, $4$ is the homological degree corresponding to the Adams filtration, and $t$ is the intern... | The 4-line is determined by Wen-Hsiung Lin in "$Ext_A^{4,*}({\bf Z}/2,{\bf Z}/2) $ and $Ext_A^{5,*}({\bf Z}/2,{\bf Z}/2) $", Topology and its Applications (2008) vol 155 no.5 pp 459-496.
He gives a basis for the indecomposable elements in $Ext_A^{4,*}$ and generators and relations for the quotient of $Ext_A^{s,*} $ ... | This old question caught my eye while looking at another question. It is worth mentioning that s= 5 is known and the decomposables in s=6 are as well, though this is unpublished.
Tai-Wei Chen,
Determination of <span class="math-container">$Ext^{5,∗}(Z/2,Z/2)$</span>,
Topology Appl. 158 (2011), no. 5, 660–A689,
DOI 10... | https://mathoverflow.net |
61,715 | [
"https://physics.stackexchange.com/questions/61715",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/447/"
] | I'm a physics tutor tutoring High School students. A question confused me a lot.
Question is:
<blockquote>
Suppose a mass less rod length $l$ has a particle of mass $m$ attached at its end and the rod is hinged at the other end in vertical plane. Another point object of mass $m$ is moving with velocity $v$ and hits... | Well you are right. The other teacher is right only if he is a considering a massive rod. Furthermore, if he is considering a massive rod, he is right <strong>only if</strong> he is considering the infinitesimal time interval <strong>during</strong> collision, not after, and even furthermore <strong>only</strong> for ... | Your teacher friend would be right <em>if the rod wasn't massless</em>.
Lets assume the rod does have some finite mass. In this case the centre of mass (COM) of the rod/attached weight system (which I'll call a pendulum from now on) would be somewhere between the attached weight and the hinge.
If the COM is not ... | https://physics.stackexchange.com |
67,962 | [
"https://mathoverflow.net/questions/67962",
"https://mathoverflow.net",
"https://mathoverflow.net/users/15819/"
] | Consider the assertion:
Every connected, but not necessarily paracompact, n-manifold is of cardinality
$2^{\aleph_0}$ (at least assuming the axiom of choice).
For n=1 this may be proved via enumeration of the short list of examples. The essential point is that while there is a Long Line, there is no Extra Long Line... | A connected Hausdorff manifold with more than one point has cardinality $2^{\aleph_0}$.
Here's a proof sketch.
For each point $x$ of the manifold, let $U_x$ be an open Euclidean neighbourhood of $x$. Define a transfinite sequence of subsets $V_\alpha$ of the manifold as follows. Choose some point $y$ of the manifold,... | Stephen's argument can also be phrased in the language of model theory. Given a connected manifold $X$, consider an elementary submodel of a large fragment of set theory $\mathfrak{M}$ that (1) contains all the reals,
(2) is closed under countable subsets, (3) contains $X$ as an element
and (4) is of size $2^{\aleph_0}... | https://mathoverflow.net |
120,876 | [
"https://security.stackexchange.com/questions/120876",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/108032/"
] | I am building a web app. It is currently not open source, but I am considering making it open source, so that others can fix bugs, improve it, so that others are not suspicious of my motives (fun to code & to create a useful tool for others - not making money) and so on. It is built on PHP and MySQL.
I am also try... | This is a good question with a simple answer:
<blockquote>
Best practices cannot be applied in every situation.
</blockquote>
The best practices of "don't tell the world what security algorithms you use" and also "don't expose your DB structure" exist as a possible fallback- just in case your code has a security fl... | Relying on keeping your schema secret to protect your system is not a good starting point. It's not Kerchoff's principle, but if the security of your system relies on the obscurity of the schema, then even if you keep it closed source and don't offer it to anyone else, you have problems.
<blockquote>
the script with... | https://security.stackexchange.com |
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